Anticathode.



E: W. KELLY.

ANTICATHO'DE. I APPLICATION FILED SEPT'.30| I916- ahwwm mum 29, 1918;

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Application filed September so, it

To all whom it may concern:

Be it known that l, ED IN W. liner-n3 a citizen of the United States, residing in the city and county oi Philadelphia, State of Pennsylvania, have invented certain new and useful improvements in Anticathodes, of which the following is a specification.

My invention relates to improvements in anti-cathodes and the like for electric vacuum tubes, and particularly anti-cathodes employed in ill-ray tubes.

In the production of Iii-rays there are employed within a highly evacuated tube or bulb a cathode, connected to the negative terminal of a source of high tension unidirectional ourrent, and an anti-cathode, which may be also the anode connected to the positiyeterminal of the source or our rent. A bombardment of the anti-cathode by a uncalled cathode-stream is induced by the electric pressure, and such boinba rd-- ment is accompanied by wasteful evolution of heat and the generation of useful it-rays.

the dh-ray art has advanced, proessively greater amounts of electric energy ave been passed through the iii-ray tube with increasing intensities of the aforementioned bombardment, necessitating from time to time improvements in the anti-cathode structure.

lit is the object of my invention to further improve anti-cathodes and to such end I provide an anti-cathode which is at once simple in structure, which shall withstand bombardment at even higher intensities than heretofore,-which shall withstand bombardmentsior longer periods, which shall'not so readily allow vaporization 01' metal which causes a change in the degree of vacuum in the tube, which shall allow immediate encryrlzation of the tube at full rate without preiminary Warming, by reduced elicitation or otherwise, and which shall materially reduoe tendency to or prevent cracking of the refractory material oi? the anti-cathode, my invention residing in an anti-cathode having some or all of these characteristics.

7 F or an illustration of some of the forms my invention may take reference is to be had to the accompanying drawing, in which:

Figure i represents in a simple way an lit-ray tube.

Fig. 2 is a side elevational view of an anticathode embodying my invention.

Fig. 3 is a longitudinal sectional view specification of letters ZEazont.

. or similarly 4. t to a on y a l.

IIilo. i illlllflll.

through an anti-ni-thode in modified term embodying my invention.

Referring to Fi 7., is an X-ray tube or bulb having into ral therewith the oath ode stem or within. which is disposed the catl'iode C electrically connected with the ere terior terminal. 53 which may be connected to the negative terminal ot a source of high potential current. The tube .lii has also a second stem 0 within which is a support cl on "which is carried the inti-cathode A, which in this case may also be the anode having; the exterior terminal 6 which may be connected with the positive terminal oi? the source of high potential current.

in. the operation oi? an li-ray. tube the cathode stream bombards the refractory metal 'll, which may be tungsten or other suitable material, and the l flbfllfdlllfilll} is accompanied by an evolution of heat at the member it and the production oi. Xrays which pass through the walls of the tube The heat generated at the member 'l. is absorl ed by the head H and from it gradually dissipated by radiation and conduction.

in the past it has been connnon to use for the heador heat absorbing; and storing member as H a mass of metal of good heat conductivity' genial-ally and almost exclusively of copper and such anti-cathodes have served Well their purpose when considering the conditions which led to their in troduction.

But l have round that by recourse to the materials and structures hereinafter deprior structures and overcoming their lirn itations.

Referring now to his". 2, the anti-cathode i l comprises the cylindrical or, otherwise shaped mass ll of iron, nickel, iron-nickel alloy, or other suitable material oi similar charactcristies. 'lo its front face, usually at an angle of degrees with its longitudh nal axis is attached the refrz-ictory clci'nont 'l which may be of tungsten or any other suitable refrarrtory material. it is Welded attached throughout the extent of its entire or substantially entire back face f to the head ll, and the union between the members T and H terms a perfect or direct thermal contact.

llhc thiclrness of the member 'l may he ill") "iii yea

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less or greater than that indicated in the drawing, and the members H and '1 may partake of other shapes and dimensions than those indicated.

In Fig. 3 the anti-cathode A is similar to that shown in Fig. 2, with the exception that the refractory member T is set into the head H, but is nevertheless welded or otherwise similarly attached so that its back face 7, and if desired also its peripheral face 9, is in direct or perfect thermal contact with the head H.

\Vhile copper has high or good heat eonductivity .72, iron and nickel are poor conductors of heat, their heat conductivities being respectively .158 (Landoldt and Bornstein) and (M2 (Landoldt and Bornstein), from which it is seen that copper has a heat conductivity from 4.5 to 5 times that of iron or nickel.

I. take advantage of this poor heat conduetivity of the head H to prevent, notwithstanding the perfect or direct thermal contact between them, rapid heat transfer from the refractory element T. Because of the poor heat conductivity of the member H the front or bombardment receiving face a of the refractory member T and its-back face f will be maintained at more nearly equal temperatures because the member H does not quickly absorb heat from the member T. This greater approximation to equality of temperature throughout the member T minimizes the difference in expansion at its front and rear faces and therefore reduces the internal strains within the member '1 which otherwise may cause it to crack or which may cause other disadvantageous effect.

Furthermore, the coefficients of linear expansion, per degree centigrade, for iron and nickel are materially less than that of cop-per, being respectively .00001092 (Landoldt and Biirnstein) and .00001012 (Landoldt and Bih-nstein), while that of copper is .0000149 (Landoldt and Bernstein). On the other hand the co-efiicient of linear expansion of tungsten is .00000336 (Coolidge). From this it is apparent that by the use of nickel 01' iron or other material of lower coefficient of linear expansion than copper, when the element T is of tungsten or other material of low co-cfiicient of linear expansion, the difference in expansion between the element T and the head H is reduced, with a further reduction of the strains imposed upon the member '1, and so further reducing the liability of cracking or other effect.

An alloy comprising 31.4% nickel and 68.6% iron has a very small co-eilicient of linear expansion, namely .OOOOOZM .(Kent), which is very closely that of tungsten, with the result that a head'H of such alloy or similar alloy will differ so slightly in coeficient of linear expansion that the strains imposed upon the tungsten member T due to such difference is practically negligible.

Furthermore, the employment for the head. H of iron or nickel or other material of high specific heat as compared to copper afi'ords, for equal masses, a relatively greater heat storage capacity thereby permitting, for a given rise in temperature of the head H, a longer or more violent excitation of the X-ray tube.

Iron and nickel both melt at higher temperatures than copper, and from this flows the additional. advantage that under intense excitation neither the iron nor nickel will vaporize as quickly as copper, and the prevention of vaporization implies the prevention of irregular uncontrollable changes in degree of vacuum of the X-ray tube.

While I have hereinbefore stated that iron, nickel or an alloy of them, may be used for the head H, it will be understood that other metals or alloys may be employed when they have one or more of the advantageous characteristics herein pointed out.

By the use of a backing H of the characteristics herein described it is possible immediately and without any preliminary passage of energy of lower quantity for gradual heating purposes to apply to an X.- ray tube at ordinary or room temperatures the full amount of energy intended or required for its operation. This immediate application of the full amount of energy is accompanied with no detrimental effects such as are observable when the member H is of copper. This advantage in favor of iron, nickel or other material of. the character herein referred to is believed to be largely due to the fact that the temperature gradient between the front face i and the 101') rear face 7 of the member T is small because of the poor heat conductivity of the member H.

While the smaller co-efiicient of linear expansi'on, the higher specific heat and the lower heat conductivity of member H are each individually of advantage in the-directions indicated, these characteristics also mutually contribute to an improvement of the behavior of the anti-cathode particu- 1 .5 larly in that, while not subject to effects hereinbefore described, a given amount of energy may be passed through the X-ray tube for a longer time and greater amounts of energy maybe passed through the X-ray tube than in the case of the anti-cathodes herein referred to having heads H of copper.

It will be understood that the term iron as herein employed includes steel and alloy steels.

What I claim is:

1. An anti-cathode comprising a head of metal of poor heat conductivity and a member of refractory metal welded directly thereto.

iiieiml comprising iroii,

' meiial comprising meenoo 2. Au anti-cathode cmupl'irsing av lllll'fib' of metal member sci NW) wi l mzisrs and Welded directly thereii u 3. An antic! nmie alloy, and :1 Pi thernml contact Wfl 'i said muss uml having a co-eiiicicnt, o1 .exlmnsiou approximately equelio alloy,

4-. An anti-cathode comprising a mass 01.

metal comprising member of metal mess. v v

5. A11 emfii-cailiode comprising a mess of iron alloy, and refractory member welded directly thereto;

b; An anti-cathode comprising a1 mass of metal comprising iron end nickel, and a refractory-member Welded directly thereto.

An enti-ceiheele Comprising a mess of iron and nickel," and :L member of tungsten welded directly thereto.

8. An enticathocle comprising a mess of iroiieiid. DlQlifQl ell-0y having e co-efiiciemof iron, and ii refractory Welded directly to said irom u'isilig a mass of rraemey member in direct;

'tl'ie-co-eliieieut of expzmsion of said szon less than and linear expansion approximately equal to.

metal having wheet conductivity materially less' than' and e specific: heal; greater then copper, and a member of refractory meineriel welded directly thereto. I r

11. A11 anti-cathode comprising a head of metalheving a co-eflicient of linear expae" a he'atvconquct vity mate i rially less than copper, and. a member of re fractor material welded direcl ly thereto. v comprising a, heeol of 12., n enticethode mete-l having a heat conductivity-materially less'than copper and a meltingpoint higher than copper, arid a member of refractory meterieijwelded directly thereto. I

In. testimony whereof I have hereunto eflixe'd my signature this 28 clay of Seph,

- .--EDWJIN W. KELLY.

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